1. Field of the Invention
The invention relates to a differential apparatus that outputs an input driving force from two side gears while allowing a difference in driving force.
2. Description of the Related Art
Differential apparatuses that output an input driving force from two side gears while allowing a difference in driving force have been used as differentials for vehicles. Examples of such differential apparatuses are disclosed in Japanese Patent Application Publication No. 2001-146952 (JP 2001-146952 A), and Japanese Patent Application Publication No. 10-16603 (JP 10-16603 A).
Differential apparatuses disclosed in JP 2001-146952 A and JP 10-16603 A include a differential gear mechanism in which two side gears mesh with a plurality of pinion gears such that the gear axis of the side gears is orthogonal to the gear axis of the pinion gears, and a pinion shaft that rotatably supports the pinion gears. In the differential apparatus disclosed in JP 2001-146952 A, the pinion shaft is supported by a differential case, and a driving force that is input to the differential case is transmitted to the two side gears via the pinion shaft and the pinion gears.
In the differential apparatus disclosed in JP 10-16603 A, the pinion shaft is supported by a cylindrical inner case, and the inner case is disposed to be movable in the axial direction in an outer case. Each of the outer case and the inner case has meshing teeth. Thus, when the inner case moves relative to the outer case to one side in the axial direction, the meshing teeth of the outer case and the meshing teeth of the inner case mesh with each other, so that the inner case and the outer case rotate together. In this meshing state, when a driving force is input to the outer case, the driving force is transmitted to the two side gears via the inner case, the pinion shaft, and the pinion gears. On the other hand, in a state in which the meshing teeth of the inner case and the meshing teeth of the outer case do not mesh with each other, transmission of the driving force from the outer case to the inner case is blocked.
That is, in the differential apparatus disclosed in JP 2001-146952 A, the differential case serves as a pinion shaft support member. Meanwhile, in the differential apparatus disclosed in JP 10-16603 A, the inner case serves as a pinion shaft support member. A washer is interposed between the inner surface of such a pinion shaft support member and the back surface of each of the pinion gears. The washer reduces the friction resistance to rotation of the pinion gear, and reduces wear of the pinion shaft support member.
When a driving force is transmitted from the pinion gear to the side gears, the pinion gear receives a meshing reaction force from the side gears. The washer is pressed against the pinion shaft support member by this meshing reaction force. The washer is also pressed against the pinion shaft support member by a centrifugal force applied to the pinion gear. Accordingly, the pinion shaft support member needs to have a sufficient strength against not only the driving force transmitted to the pinion shaft, but also the pressing force applied from each pinion gear. This is an obstacle to reducing the weight of the pinion shaft support member, and hence is a constraint on improving the vehicle fuel efficiency by reducing the weight of the differential apparatus.